1. Field of the Invention
The present invention generally relates to a water treatment method and a water treatment device for muddy water used in water excavation engineering which is broadly employed in piling works for making ground formations and in underground continuous wall making works, and for industrial waste water discharged from various works. More particularly, the present invention relates to a method and device which can perform a regeneration treatment for the used muddy water in order to reuse it and a dehydration treatment for the waste muddy water and industrial waste water to reduce the weight.
2. Description of the Prior Art
Water excavation engineering has been well known to realize low noise and low vibration and is thus broadly employed in various civil construction works, such as piling work, underground continuous wall making work, water shield work, water drive work, and so on. For example, an earth drill method, a reverse circulation method, or BH method is used in combination with the water excavation engineering to perform the piling work, and a bucket method or a rotary method is used in combination with the water excavation engineering to perform the underground continuous wall making work.
In the water excavation engineering, natural muddy water, bentonite muddy water, polymer muddy water or the like, is used as a stabilizer for excavating the hole, a conveying fluid for excavated substance, and a substitute fluid for unhardened concrete supplied into the excavated space. Furthermore, the muddy water is often used for cooling an excavation machine and preventing the underground water from gushing into the excavated space. Therefore, the quality of the hardened concrete, the construction period, and the cost and safety of the work depends on the management and control of the muddy water under construction.
The management and control of the muddy water is carried out in response to various factors representing physical properties of the muddy water, such as viscosity, specific gravity, filtrated water amount, muddy layer thickness, sand percentage, pH and so on. Generally, the physical properties of the muddy water are so controlled as to keep the values of these factors within a predetermined range or less than a predetermined value. Particularly, the specific gravity of the muddy water should be lowered as much as possible while an excavated hole is stable in order to maintain construction quality at a desired level. It is desirable to keep the specific gravity of ordinarily used muddy water at no higher than about 1.2 during excavation and at no higher than about 1.1 during the pouring operation of unhardened concrete. When the specific gravity of the muddy water exceeds the above values, the quality of the muddy water becomes poor, which results in a lower excavation efficiency and involves slime formed in the concrete during the pouring operation of unhardened concrete. Accordingly, it is required that muddy particles such as slime, be removed from the muddy water as much as possible.
Conventionally, the muddy particles are removed from the muddy water by means of natural sedimentation or some kind of mechanical apparatus, such as a cyclone, to lower its specific gravity. However, they cannot exert a sufficient specific gravity lowering effect because they cannot remove fine particles of less than 74.mu.. In detail, the muddy particles and slime are removed by a commonly used apparatus using a combination of a vibration type sieve and a liquid cyclone whose classification point is about 74.mu.. This classification point represents the particle size when the contents included in the under flow and the over flow are at a ratio of 50% : 50%. In the above described sand separator using a combination of a vibration type sieve and a liquid cyclone, 50% of fine sand particles are included in the overflow. Thus such a conventional apparatus cannot remove fine sand and muddy particles of less than 74.mu.. When the ground which is excavated is mainly composed of fine sand, silt and clay, such fine sand, silt and clay particles remain in the muddy water and therefore the specific gravity of the muddy water cannot be lowered. The once used muddy water with the higher specific gravity can not be reused.
In conventional muddy water using excavation engineering, the muddy water with an undesirable high specific gravity, which includes much fine muddy particles caused by excavation work, is partially or wholly replaced by newly prepared water. That is, the muddy water with the higher specific gravity is disused. These conventional methods, however, provide some disadvantages, such as the replacing operation requires a relatively long time, resulting in extension of the construction period and cost for newly prepared water.
Various construction works generate much turbid water as industrial waste water, including a mixture of surface water, underground water or rain water, and sand, muddy particles, cement or the like, for example, turbid water generated by tunnel work; washed water by aggregate producing work; turbid water by rain water during ground formation work; turbid water by dredging and reclaiming works; waste water from a batcher plant; turbid water by pouring work of concrete; grout; turbid water by boring work; oil containing waste water leaked from construction machines; iron containing waste water by water replacement; and so on.
Since the waste muddy water is treated as industrial waste sludge, it should be subjected to proper treatment before final disposal in order to avoid environmental pollution. Furthermore, the above described industrial waste water should also be treated to avoid water pollution. This treatment, however, is complicated and results in an increase in cost.
Conventionally, the waste muddy water is subjected to a dehydration treatment using a filter cloth in order to decrease the weight of the waste sludge. The filter cloth, however, is easily blocked with fine muddy particles of the waste sludge and thus the dehydration ability becomes poor in a short time. Therefore the dehydration treatment can not effectively treat the waste muddy water.
On the other hand, the inventor provides a vertical type muddy water separator which can remove muddy particles from muddy water and industrial waste water generated by excavation work to decrease the specific gravity of the used muddy water and industrial waste water for reusing them, and can dehydrate the muddy water and industrial waste water to decrease its weight for final disposal. The muddy water separator comprises a stationary casing provided with an outlet port and an inlet port, a movable inner basket which is movably interposed in the stationary casing and whose cylindrical wall is not perforated, a cross shape arm arranged at an annular bottom of the basket, and a rotary drive shaft fixed at the cross point of the cross shape arm to pivotably suspend the basket within the stationary casing. When the rotary drive shaft is rotated at a high speed, the muddy water is supplied into the stationary casing through the inlet port. Muddy particles of the muddy water are sedimented and adhere to the inner cylindrical wall so that the solid part and the liquid part of the muddy water can be separated. This separator requires that the solid part from the basket wall be removed and temporarily stops the solid-liquid separation work whenever the solid part adhering to the basket wall reaches its maximum level.
Conventionally designed separators are not equipped with a sensory means for detecting the maximum level, and thus require skilled workers to sense the maximum level and to remove the solid part from the separator wall. However, since skilled workers do not always correctly detect the maximum level, the removing work may be untimely carried out. When the adhered solid part does not reach the maximum level, such untimely removal causes the work efficiency of the separator to be lowered on the other hand, when the adhered solid part exceeds the maximum level, the muddy water can not be treated by the separator and is directly discharged out of the water treatment system.